Thin-walled articles, e.g. foils or other sheets, having a maximum thickness of 3 mm, form a considerable part of the product assortment of the rubber and plastics industry. The aforesaid flat articles may be formed from only one polymeric or rubber component or from their various mixtures. They can be, in addition, single-layer or multilayer, and the further layers may be formed again from polymers or rubber, or from various supports, as for instance woven or non-woven fabrics, etc. The physical, mechanical and chemical behavior of the aforesaid articles is influenced by the types of components used and by their finishing.
A great deal of the production of foils and other thin sheets represents artificial leathers, which are not only up to, but even surpass the natural material in appearance and in many physio-mechanical properties. The low sorption of water (Absorptivity) and the small or non-existent water vapor permeability prevent the broad application of previous artificial leathers in shoe and glove making, although these properties are advantageous in other areas of application, e.g., in the packaging industry. Rubber sheeting has similar unsuitable properties for use in the shoe industry, glove making, etc.
Numerous methods have been tried in order to gain the desired permeability, from the purely mechanical ones (e.g. perforating) to those affecting the microstructure of the articles formed (microporous materials, poromers). These methods are conventional and may be used for practically all types of macromolecular materials. One of the methods for the preparation of permeable materials is the incorporation of soluble inorganic salts (NaCl) or organic compounds (sugars). These components are removed either in the formation of the article or in subsequent operations by washing with a suitable solvent (usually with water), thereby leaving cavities or channels and providing permeability for water vapor.
Certain improvements in the absorptivity of the plastic and rubber foils can be achieved by the dressing thereof with hydrophilic agents, e.g. vegetable proteins, some water-soluble polymeric materials, as for example poly(ethylene oxide), etc. However, such a treatment is mostly effective for a limited period of time only.